Display apparatus having drum indicators, controlled by individual synchronous motors



M. BROWN 3,184,731

6 Sheets-Sheet 1 May 18, 1965 DISPLAY APPARATUS HAVING DRUM INDICATORSCONTROLLED BY INDIVIDUAL SYNCHRONOUS MOTORS Original Filed Oct. 30, 1953FIG. 1

OMNI RANGE RECEIVER DISTANCE COMPUTER FIG. 2

r/wf/vrae I M/L TO/V BROWN May 18, 1965 M. BROWN DISPLAY APPARATUSHAVING DRUM INDICATORS CONTROLLED BY INDIVIDUAL SYNCHRONOUS MOTORSOriginal Filed Oct. 30, 1953 6 Sheets-Sheet 2 FIG. 3

FIG. 4

/A/ 1/6 A/ 706 M/L TO/V BROWN May 18, 1965 M. BROWN 3,184,731

DISPLAY APPARATUS HAVING DRUM INDICATORS CONTROLLED BY INDIVIDUALSYNCHRONOUS MOTORS Original Filed Oct. 30, 1953 6 Sheets-Sheet 3 III/II1 1/ II I FIG. 6

M/ O OWN May 18, 1965 M. BROWN 3,184,731 DISPLAY APPARATUS HAVING DRUMINDICATORS CONTROLLED BY INDIVIDUAL SYNCHRONOUS MOTORS Original FiledOct. 30, 1955 6 Sheets-Sheet 4 FIG. 7

FIG. 9

m/wizvrola M/L TON BROWN BVW 6770 may M. BROWN May 18, 1965 DISPLAYAPPARATUS HAVING DRUM INDICATORS CONTROLLED BY INDIVIDUAL SYNCHRONOUSMOTORS Original Filed 001;. 30, 1955 6 Sheets-Sheet 5 INVENTOR.

M/LTON BROWN May 18, 1965 BROWN DISPLAY APPARATUS HAVING DRUM INDICATORSCONTROLLED BY INDIVIDUAL SYNGHRONOUS MOTORS Original Filed Oct. 30, 19556 Sheets-Sheet 6 INVENTOR. B 14/L7'ON BROWN United States Patent "Ice3,184,731 DKSPLAY APPARATUS HAVING DRUM ENDEA- TGRS, CONTROLLED BYKNDIVHDUAL SYN- QHRQNOUS MUTORS Milton Brown, Glen Rock, Null, assiguorto The Bendix Corporation, a corporation of Delaware Continuation ofapplication Ser. No. 339,390, Oct. 353, 1953. This application Sept. 1,1961, Ser. No. 137,937 2 Claims. (Cl. 340-315) The present applicationis a continuance of US. application Serial No. 389,390, filed October30, 1953, and now abandoned, by Milton Brown and assigned to the BendixAviation Corporation, now by change of name The Bendix Corporation.

The invention relates to electrically operated indicating systems andparticularly to systems in which drum counter type indicators are used.

An object of the invention is to provide an improved arrangement for theelectrical operation of one or more drum counter indicators located at adistance from a main indicator. One purpose is to provide novel meansfor the electrical actuation of remote counters and, in particular, anelectrical system that will be simpler and less expensive than those nowin use.

A further object is to eliminate the necessity for employing amplifiersand servomotors in the actuating circuits, and to employ synchros forthe direct operation of remote indicators. This presents a seriousproblem, since the usual small synchro suitable for this purpose doesnot develop enough power for satisfactory operation of the usual drumcounter mechanism. Another object of the invention is the origination ofa counter construction that can be efliciently operated by low powersynchros. This is accomplished in general by providing a novel drumstructure, including a direct synchro mounting; and a specific featureis the mounting of one or more synchros within the drums of a counter soas to produce an eflicient and compact arrangement in which the directdrive connection between a synchro and the associated drum makes itpossible for the synchro to rotate such drum directly. A further featureof this construction is the independent operation of each drum.

A related object is the development of a novel drum counter having twoindependent drums, each directly rotated by a synchro within the drum;and in an improved form, the incorporation of additional drums, adaptedfor rotation either by a synchro or by other types of electricalactuating devices.

In some types of installation the last drum of the indicator, such asthe hundreds drum in a three drum counter, will never be required toexpose the higher digits. For instance, in automatic distance indicatingsystems for aircraft which show the number of miles to a destination,certain systems are not operative beyond two hundred miles, in whichcase the hundreds drum requires only the 0 (or a blank space) and thedigit 1. In systems which operate up to four hundred miles, the hundredsdrum requires only the digits 1, 2, and 3. A purpose of the invention isto provide a remote indicator arrangement suitable for such systems,which includes a simplified and less expensive construction than thatwhich employs synchro drive for each drum, but which will impart to thehundreds drum of a remote indicator the limited movements which satisfysuch systems.

When operating a receiver synchro to locate its rotor in variousselected angular positions by providing the required voltages to thewindings of the synchro stator, the accepted practice is to connectthese windings in series with corresponding windings of the stator of atransmitter synchro, an arrangement commonly called back to back,

3,184,731 Patented May 13, 19.65

and thus locate the transmitter rotor, energized from the same source asthe receiver rotor, in the desired positions. An object of the inventionis to provide novel arrangements for applying the correct voltages tothe receiver stator windings to locate the rotor in a desired sequenceof positions. Related objects are to provide a switching system for thispurpose; to accomplish the indicated objects in a simplified manner bygrounding one stator winding; and to simplify the system by employing aphase reversing arrangement.

Another object is to provide a novel warning signal, operative toindicate failure of power or signals.

The foregoing and other objects and advantages of the invention willappear more fully hereafter from consideration of the detaileddescription which follows, considered in conjunction with theaccompanying drawings, in which one embodiment of the invention andcertain modifications thereof are illustrated. It is to be expresslyunderstood, however, that the drawings are for the purposes ofillustration and description and are not to be construed as defining thelimits of the invention.

Referring now to the drawings for a more detailed showing of a noveldistance indicating system embodying the invention:

FIG. 1 is a schematic diagram of a distance indicating system, includinga main drum counter indicator, a similar remote indicator, and anarrangement for actuating the latter indicator;

FIG. 2 is a front elevation of the main indicator, showing a warningsignal in operative position;

FIG. 3 is an end elevation of the main indicator;

FIG. 4 is a top view of the main indicator;

FIG. 5 is an end elevation of the remote indicator counter and actuatingdevices with the casing removed, shown in central vertical section;

FIG. 6 is a top view of said remote indicator with the casing and theleft half of the drum counter shown in central horizontal section;

FIG. 7 is an end elevation of the remote indicator, similar to FIG. 5,showing an alternative construction;

FIG. 8 is a diagram of drive arrangements for the hundreds drum of theremote indicator, including certain modifications;

FIG. 9 is an end view of a switch cam in FIG. 8;

FIG. 10 is a graph of voltages of synchro stator windings for differentrotor positions;

FIG. 11 is a diagrammatic face view of another form of hundreds drumdrive; and

FIG. 12 is a vertical central section through the switch structure shownin FIG. 11.

Referring first to FIG. 1, the invention is illustrated in itsapplication to an automatic distance indicating system of establishedtype widely used on aircraft, which receives beacon signals from anomnirange transmitter, automatically computes the distance to thetransmitter and operates a drum counter indicator to show at all timesthe distance in miles between the aircraft and. the transmitter. Thisarrangement includes a receiver and distance computer 1d, which operatesthrough shaft 11 a standard type of drum counter 12. The receiver andcomputer are so well known that they are shown only diagrammatically.The indicator 12 has the usual units drum 13, tens drum 14 and hundredsdrum 15, with interposed Geneva movement drive of standard type, notshown. The indicator 12 is carried by a U-shaped mounting plate 16(FIGS. 2-4) provided at the front with bolts 17 and shielding strips 18having end portions curved around bolts 17 and central portionsextending across the spaces between and in close alignment with thesurfaces of drums 13, 14, 15, arranged to hide the actuating mechanismbetween the drums.

A signal is provided on the main indicator 12 for warning the observerwhen power failure, or the weakness or lack of signals picked up byreceiver 10, prevents said receiver from operating properly theindicator 12, in which case the mileage shown thereon would be anunreliable indication of the distance of the transmitter. In the formillustrated, this warning signal 19 comprises a metal strip 20 withinturned end portions 21 pivoted on the shaft 22 of the indicator 12.The strip 26 is located just above the dr'um'surface, and may be swunginto or out of position in line with the visible numerals on the drums,being advantageously painted a bright color to attract attention. In theform illustrated in FIGS. 2, 3 and 4 the signal strip 20 is narrow andpermits observation of the numerals at all times.

Means actuated by the power in the receiver 10 is provided for swingingsignal 19 into and out of operative position. In the form illustrated inthe latter figures, a pinion 23 fixed to a signal strip end portion 21meshes with a gear sector 24 on a lever arm 25 mounted on pivot 26carried by the mounting plate 16, arm 25 having an end pivoted toextension 27 of L-shaped arm 28 attached to the plunger 29 of solenoid30. The solenoid and the 'mounting plate 16 are attached to frame plate31. A spiral spring 32 hearing against plate 31 and arm 28 is arrangedto swing the lever arm 25 normally into position where the signal strip20 overlies the visible numerals on the indicator 12.

When solenoid is energized it retracts plunger 29 against the pressureof spring 32, swinging the signal strip 20 laterally out of view throughwindow 33. The solenoid energizing circuit 34 (FIG. 1) extends to thereceiver 10, and is connected in series with the signal circuit therein,so that if the signal becomes too weak to operate indicator 12 properly,or is missing, or if the power should fail and prevent any signaloutput, solenoid 30 would be de-energized, permitting spring 32 to shiftsignal 19 into operative position. Moreover, the signal will retain suchposition after the receiver 10 is initially turned on until the receiverhas heated up and is operating with enough power to position indicator12 properly, so that premature reading of the indicator is prevented.

It is generally important to provide a plurality of auxiliaryindicators, located at various points distant from the main indicator 12and which will at all times have the same reading, a system that isnecessary in larger aircraft, for instance. An improved arrangement foroperating remote indicators of this type is shown. Referring again toFIG. 1, a remote drum type indicator 37 is provided with a units drum38, a tens drum 39, and a hundreds drum 40 corresponding to drums 13, 14and 15 of the main indicator 12. As a standard type of drum counter isgenerally used for the indicator 37, a servo having suflicient power todrive the indicator would be required, together with a servo operatingcircuit which would include an amplifier to furnish the necessaryoperating energy. This is avoided by providing at the main indicator 12a remote indicator drive including an electrical actuating element foreach of the drums of the remote indicator 37, and at the remoteindicator 37 a separate drive for each of said drums operated by one ofsaid elements. The actuating elements 41, 42 and 43 are driven fromshaft '11, as by bevel gears 44 and shaft 45. These elements may besynchros connected through step drive gearing 46, which may be of themutilated gear type rotating in unison with the general drive of thedrums of the main indicator '12,'so that the rotor of the tens synchro42 will shift A of a revolution for each revolution of units synchro 41attached to shaft 45, and the rotor of synchro 43 will move of arevolution for each revolution of the tens synchro 42. Obviously otherwell known drive arrangements may be employed.

The drums 38, 39 and 40 of remote indicator 37 are independentlymounted, and each is connected to and rotated by a drive elementelectrically actuated by the corresponding synchro 41, 42, or 43. In theform illustrated, as shown in FIGS. 5 and 6, a units drive synchr'o'47is mounted in the frame 48 of the remote indicator 37, coaxial with andextending into the units drum 38, whose transverse flange 49 is mountedon the shaft 50 of the rotor of synchro 47, said flange advantageouslybeing defiected axially so that it lies close to the longitudinal centerof the indicator 37. The tens drive synchro 51 is similarly mounted onframe 48, extending axially into the frame; and the central flange 52 ofthe tens drum 39, which is bent to lie in about the longitudinal centerof the indicator 37, is mounted on the rotor shaft 53 of synchro 51.

The hundreds drum 40 has a centrally apertured end flange 54 rotatablymounted on the frame 48. In the form illustrated a flat ring gear 55 isfixed to flange 54 andto cylinder 56, rotatably fitted around acylindrical bearing 57 on frame 48.

A suitable hundreds drum drive element, engaging ring gear 55, isprovided. In the arrangement illustrated in FIGS. 5 and 6 this elementcomprises a synchro 58 mounted on the frame 48 and having a pinion 59 onits rotor shaft 60 engaging the ring gear 55.

In this embodiment the units drive synchro 47, actuated by unitstransmitter synchro 41, will rotate the remote indicator units drum 38in synchronism with the main indicator units drum 13; the tens drivesynchro '51, actuated by tens transmitter synchro 42,'will rotate theremote indicator tens drum 39 in synchronism with main indicator tensdrum 14; and the hundreds drive synchro 53, actuated by hundredstransmitter synchro 43, will rotate the remote inidcator hundreds drum40 in synchronism with the main indicator hundreds drum 15. In thismanner all movements of the main indicator drive shaft 11 will operatethe remote indicator 37 in exactly the same way as the main indicator12.

A device having the double function of a shield and a warning signal islikewise provided for the remote indicator 37, and operates in the samemanner as the signal on the main indicator. It comprises a signal andshield structure 61 including a strip 62 with an inturned end 63 onwhich is mounted ring gear 64 fixed to cylinder 65 rotatably supportedby cylindrical bearings 66 on the frame 48. A gear sector 67 meshingwith ring gear 64 is mounted on lever arm 63 fixed to pivot block 69rocking on pivot 70 on frame 48, and fixed at its other end to rockingarm 71 engaging plunger 72 of solenoid 73, whose winding is connected inparallel with the winding of the main indicator solenoid 30 throughleads 74 (FIG. 1) and across the energizing circuit 34. A'tension spring75 engaging oifset arm 76 of arm 71 normally biases the gear sector 67into a position where the signal and shield strip 62 overlies thenumerals on the drums of indicator 37, except when solenoid 73 isenergized and rocks the gear sector 67 to shift the'signal and shieldmember 62' into an invisible position rendering the indicia on drums 33,39 and 40 visible to view through a window 77. In the form illustratedin FIGS. 5 and 6 the strip 62 is wider than in the form shown in FIGS.2-4, so that it constitutes in effect a shutter which completely hidesthe drums and the numerals on the drums from view through the window 77,as shown in FIGURE 5, upon deener- 'gization of the solenoid 73.

The structure illustrated in FIGURES 1 through 6 V 'matter of a U8.application for patent, Serial No. 846,122,

filed October 13, 1959, by Milton Brown, as a division of the US.application Serial No. 389,390, and assigned to Bendix AviationCorporation.

Where only a limited number of digits on the hundreds drums will ever beused, as in the instances heretofore indicated, an arrangement isprovided to replace synchro 43 for actuating the remote indicatorhundreds drum which is simpler and substantially less complicated andexpensive than the synchro arrangement that has been described. One formof this arrangement employs in place of synchro 43 a rotary switch, andin place of the hundreds drive synchro 53 a simpler electricallyactuated device for rotating the hundreds drum 40. In one embodiment ofthis arrangement, shown in FIGS. 7 and 8, the drive synchro 43 isreplaced by a similarly mounted rotary switch, which turns the hundredsdrum 40 through solenoid actuated gearing in the same general manner asthat described in connection with the operation of signals 19 and 61.

The solenoid actuating arrangement is illustrated in FIG. 7, and issubstantially the same as the signal operating mechanism shown in FIGS.5 and 6. The ring gear 55 is engaged by a gear sector 78 on lever arm 79fixed to pivot block 80 rotating on pivot 81 mounted on frame 48, block80 carrying rocking arm 82, against which the plunger 83 of solenoid 84bears. Gear sector 78 is normally biased by a spring 85 engaging arm 86on pivot block 80 so as to maintain the gear sector 78 and hundreds drum40 in the position where the blank space or 0 is visible through thewindow 77. When solenoid 84 is energized, the gear sector 78 is rockedto shift the drum 40 and bring the digit 1 into view.

A switch suitable for the proper energizing of solenoid S4- is rotatablymounted in place of synchro 4'3, and is driven by intermittent gearing16'. The type of switch 87 shown in FIG. 8 will be described since ithas certain advantages that will appear hereafter. In this constructiona block 88 is provided on its cylindrical face with two annular metalconducting strips 89, 90 having contact teeth 91 extending alternatelyin spaced relation into a central contact zone 92. Strips 89 and 90 areinsulated, as by forming block 88 of insulating material. Slidingcontact connections with strips 89 and 90 are provided. As shown, brush93 maintains engagement with strip 89, brush 94 with strip 90, and brush95 is located in the zone 92 in contact with the teeth 91. Brushe 93 and94 are connected across a suitable source of electrical energy. Whenswitch 87 is used to operate solenoid 84, brushes 93 and 94 areconnected across a DC. potential source 96, this arrangement beingindicated in dash lines.

Hundreds drum 40 may likewise be rotated through synchro 58 by a simplercircuit arrangement which can be adapted to different requirements as tothe numerals which are to be displayed by the drum, and which eliminatesthe use of synchro 43. An arrangement of this type, suitable forpositioning drum 40 to display either the zero space or the numeral 1,is shown in FIG. 8. In this arrangement the ends of secondary 97 of thetransformer 98, energized from A.C. source 99, are connected to brushes93 and 94, as shown. Stator 10-0 of synchro 58 has winding 101 grounded,winding 102 connected to an intermediate point 103 of secondary 97, thecenter point of which is grounded, and the third winding 104 connectedto brush 95. With this arrangement the voltage applied to stator winding104. will alternate between the voltages at the ends of transformersecondary 97, while the voltages at windings 101 and 102 remain fixed.This will create two separate fields for rotor 105 of synchro 58,connected to source 99 by leads 106 and 107; and the voltages areselected so that these fields will be at right angles, as hereafterexplained. Under these conditions rotor 105' and drum 40 will alternatebetween two positions at right angles to each other; and by locating thezero or blank space and the numeral 1 at appropriate points on drum 411,these points will be properly located in visible position as the switch87 rotates.

Under certain conditions it is desirable to expose more than two digitson drum 40. In one aerial navigation system in present operation, fourpositions are required, carrying the digits 0, 1, 2 and 3 respectively.In one arrangement suitable for this type of system, illustrated inFIGS. 8 and 9, the cylindrical block 88 is provided with a cam surface108 arranged to engage the plunger 109 of a standard plunger-actuatedreversing microswitch 110 inserted in leads 106 and 107 from rotor 105.Cam 108 is located so that it will engage switch plunger 109 and throwswitch 110 when block 83 rotates one step after the numeral 1 has beendisplayed on drum 40. This will reverse the phase of the voltage appliedto rotor 105 during the next two steps, when digits 3 and 4 aredisplayed, so that the positions of rotor 105 will be 180 offset fromits positions during the two preceding steps.

The switch 87 is arranged for the described type of op eration, havingfour equal contact teeth 91, the cam 108 being circumferentially alignedwith two consecutive teeth which locate rotor 105 and drum 40 inpositions for display of the digits 3 and 4. Drive gearing 46' istherefore constructed in known manner to rotate switch 87 through 90 foreach revolution of tens drum 39. It will be evident, however, that thisswitch system is' equally adapted to the location of rotor 105 in agreater number of positions by providing additional contacts for thebrushes, connected to the proper voltages.

The voltages applied to each of the three windings of stator 100 inorder to position rotor 105 and its associated hundreds drum 40 in asequence of selected positions, such as those that have been described,can be determined by calculating the relative voltages to be applied towindings 102 and 104, when winding 101 is grounded, to produce resultantfields that will locate rotor 105 in any desired angular position, inaccordance with formulas known to those skilled in this art. The voltagerelationships of the windings under these conditions throughout acomplete revolution of rotor 105 is a sine function, as indicated inFIG. 10. From this figure it will be evident that in the firstarrangement described, two positions of rotor 105, offset by 90", can beobtained by properly locating point 103 on the transformer secondary 97,and by designing this secondary to have the proper voltages at itsterminals. These two positions are indicated on the FIG. 10 graph by theletters A, A and B, B respectively. It will also be evident from thisfigure that by reversing the phase of the voltage applied to rotor 105,its two succeeding positions, indicated by C, C and D, D' on FIG. 10,will be offset 180 from its two initial positions.

Other switching arrangements may be utilized for applying to windings102 and 104 the proper voltages for locating rotor 105 and drum 40 inany desired sequence of positions, either directly or by using areversing switch for simplification purposes in the manner alreadyillustrated, taking advantage of the fact that the two halves of thevoltage curve for each winding of the stator 100 are identical exceptfor reversal of phase. One generalized arrangement of this type isillustrated in FIGS. 11 and 12, designed to locate drum 40 in tensuccessive equal 1y spaced positions for the display of the digits zerothrough nine. In this embodiment stationary switch disk is mounted inplace of block 88, with the drive shaft 116 from gearing 45 journaled indisk 115, said gearing 16 being of the standard ten step type. Mountedon the disk face are inner contact ring 117 and outer contact ring 118concentric with shaft 116. Sectors in an outer series 119, concentricwith said shaft, are connected to appropriate points on transformersecondary 97.

Ten equally spaced sector positions are provided in this arrangement;but two opposite pairs of sectors are joined to form longer sectors forreasons hereafter indicated. Long sector 120 is connected to point 121at one end of secondary 97. Short sectors 122., 123 and 124 areconnected respectively to the upper intermediate point 125, centergrounded point 126 and lower intermediate point 127 on secondary 97',while the other long sector 120 is connected to the lower secondaryterminal 129.

The remaining 3 short sectors 130, 131 and 132 are cross- 'connectedrespectively to sectors 124, 123 and 122.

Shaft 116 carries contact arm 133, on which is mounted a brush 134positioned to engage sectors 119, and a brush 135 bearing. against innercontact ring 117, the brushes being electrically connected. A secondcontact arm 136 fixed to shaft 116 carries brush 137 arranged to contactsectors 1'19, and electrically connected brush 138 bearing against outercontact ring 118. Inner ring 117 is connected to stator winding 102through lead 139, while outer ring 118 is connected to stator winding104 through lead .The arrangement illustrated will locate rotor 105 andthe hundreds drum 40 in ten equidistant positions for the display of theten digits, as already indicated; and the illustrated position ofcontact arms 133 and 136 is that at which the digit zero will beexposed. The voltages at the points 121, 125, 126, 127 and 129 onsecondary '97 are selected to maintain the proper relationships betweenthe voltages ,of the three windings of stator 160 in order to locaterotor 195 properly in the indicated 10- cations; and these positions forthe various digits have been indicated on the graph of FIG. 10, and inFIG. 11.

It will be noted that the voltages for successive positions at the peaksof the curves will be the same. Consequently the corresponding sectorsare combined to form thelong sectors 120 and 128; and the voltages atthe three points following each peak are reproduced in inverse orderfollowing the next peak. This relationship is the basis for thecross-connection of the shorter sectors 119, and for the possible use ofa reversing switch in the manner already indicated. Moreover, the twocurves for windings 102 and 104 respectively are identical, except fortheir offset positions, and the angle between arms 133 and 136 isselected to correspond to the angular distance by which these curves areelectrically offset.

While the embodiment shown in FTGS. 11 and 12 produces ten drumpositions, it is evident that it can be utilized to position rotor 105in any sequence of positions, simply by connecting sectors 119 to pointshaving the proper voltage values on secondary 97 or other source ofvariable voltage. Moreover, these rotor positions need not be equallyspaced, nor need they involve rotation always in the same direction.

Although but one main embodiment of the invention has been illustratedand described in detail, together with certain modifications of partsthereof, it is to be expressly understood that the invention is notlimited to the specific disclosure. Various additional changes may bemade in the design and arrangement of the parts without departing fromthe spirit and scope of the invention as the same will now be understoodby those skilled in the art.

I claim:

1. For use in an electrical indicator control system, a drum indicatorcomprising a frame, a series of three coaxial rotatable drums bearingindicia thereon and mounted on the frame, and drum rotating apparatusarranged to bring selected indicia into viewing position,

including a synchro mounted on the frame at one end 69 of the series andextending into one of said drums, said synchro having a rotor engagingone of the drums, an-

other synchro mounted on the frame at the other end of the series andextending into another of said drums, said other synchro having a rotor.engaging another drum, a third synchro'having a rotor and a driveelement engaging the rotor of the third synchro with the third drum, awindow through which the indicia of' said drums may be visible, ashutter member pivotally mounted concentrically with said drums andnormally positioned relative to said window so as to completely shieldsaid indicia y from view through saidwindow,'motor means carried.

by said frame, and a source of electrical energy to effectively,energize said motor means upon the indicator control system being in anoperative condition, said motor means connected to the shutter memberand arranged to cooperate with the indicia bearing drums so as to shiftsaid member out of said normal shield position in response to theeffective energization of said motor means so that said selected indiciaon said drums are thereupon rendered effective and visible through saidwindow so long as the indicator control system continues in saidoperative condition.

2. Foruse in an electrical indicator control system, a drum indicatorcomprising a frame, a series of three coaxial rotatable drums bearingindicia thereon and mounted on the frame, and drum rotating apparatusarranged to bring selected indicia into viewing position, including asynchro mounted on the frame at one end of the series and extending intoone of said drums, said synchro having a rotor engaging one of thedrums, 'another synchro mounted on the frame at the other end of theseries and extending into another of said drums, said other synchrohaving a rotor engaging another drum, a third synchro having a rotor anda drive element engaging the rotor of the thirdsynchro with the thirddrum, a window through which the indicia of said drums may be visible, ashutter member pivotally mounted concentrically with said drums andnormally positioned relative to said window so as to at least partiallyshield said indicia from view through said window, motor means carriedby said frame, and a source of electrical energy to effectively energizesaid motor means upon the indicator control system being in an operativecondition, said motor means connected to the shutter member and arrangedto cooperate with the indicia bearing drums so as to shift said memberout of said normal shield position in response to the effectiveenergization of said motor means so that said selected indicia on saiddrums are thereupon rendered effective and visible through said windowso long as the indicator control system continues in said operativecondition.

References Cited by the Examiner UNITED STATES PATENTS NEIL C. READ,Primary Examiner.

IRVING SRAGOW, Examiner.

1. FOR USE IN AN ELECTRICAL INDICATOR CONTROL SYSTEM, A DRUM INDICATORCOMPRISING A FRAME, A SERIES OF THREE COAXIAL ROTATABLE DRUMS BEARINGINDICIA THEREON AND MOUNTED ON THE FRAME, AND DRUM ROTATING APPARATUSARRANGED TO BRING SELECTED INDICIA INTO VIEWING POSITION, INCLUDING ASYNCHRO MOUNTED ON THE FRAME AT ONE END OF THE SERIES AND EXTENDING INTOONE OF SAID DRUMS, SAID SYNCHRO HAVING A ROTOR ENGAGING ONE OF THEDRUMS, ANOTHER SYNCHRO MOUNTED ON THE FRAME AT THE OTHER END OF THESERIES AND EXTENDING INTO ANOTHER OF SAID DRUMS, SAID OTHER SYNCHROHAVING A ROTOR ENGAGING ANOTHER DRUMA THIRD SYNCHRO HAVING A ROTOR AND ADRIVE ELEMENT ENGAGING THE ROTOR OF THE THIRD SYNCHRO WITH THE THIRDDRUM, A WINDOW THROUGH WHICH THE INDICIA OF SAID DRUMS MAY BE VISIBLE, ASHUTTER MEMBER PIVOTALLY MOUNTED CONCENTRICALLY WITH SAID DRUMS ANDNORMALLY POSITIONED RELATIVE TO SAID WINDOW SO AS TO COMPLETELY SHIELDSAID INDICIA FROM VEIW THROUGH SAID WINDOW, MOTOR MEANS CARRIED BY SAIDFRAME, AND A SOURCE OF ELECTRICAL ENERGY TO EFFECTIVELY ENERGIZE SAIDMOTOR MEANS UPON THE INDICATOR CONTROL SYSTEM BEING IN AN OPERATIVECONDITION, SAID